Regular users of cannabis could be putting themselves at risk of stroke, while they are still young, indicates a case report, published in the Journal of Neurology Neurosurgery and Psychiatry.

Illicit drug use is known to be associated with an increased risk of stroke in young users, with heroin, cocaine, and speed (amphetamines) the most frequently implicated.

The patient was a 36 year old primary school teacher, who had been a sporadic user of cannabis in the past. He had no known risk factors for stroke, did not use other drugs, and only drank occasionally.

The first incident occurred after he had smoked a considerable amount of cannabis combined with three or four drinks at a party. He lost his ability to speak, which was followed, a few hours later, by convulsions.

A brain scan revealed one patch of bleeding and another blood clot, but no evidence of narrowed/furred up arteries. He was treated, and recovered.

A year later, after another bout of cannabis smoking, he again lost his ability to talk and experienced weakness on one side of his body (hemiparesis). A brain scan revealed a further small patch of bleeding as well as another blood clot, but in different areas from before.

The man refrained from using cannabis for 18 months, but then smoked a reasonable amount in one go, which he combined with three or four drinks. This was followed by an inability to recognise sounds, a condition known as auditory agnosia.

A brain scan revealed a patch of bleeding as well as the damage left by the previous bleeds.

The behavioural abnormalities and increased risk of schizophrenia, associated with frequent cannabis use, are well known, say the authors. But less well known, and no less important, are the cardiovascular effects.

These include rapid heart beat (tachycardia), excessively high or low blood pressure, and the decreased oxygen carrying capability of red blood cells. Cannabis also quadruples the risk of a heart attack within an hour of consumption.

They are at pains to point out that despite the widespread use of cannabis, there have only been 15 other cases of stroke, which have been linked to cannabis consumption.

But they conclude: "Cannabis is not as safe a drug as many believe...Future studies will be needed to clarify the role of cannabis as a stroke risk factor, as it could be underestimated."

An accompanying editorial, which discusses the possible mechanisms for the drug's impact on the cardiovascular system, suggests that recreational users of cannabis should be told more about the potential risks to their health.

"The therapeutic potential of cannabis and its derivatives should be rigorously evaluated and the benefit to risk ratio taken into account before authorising their medical use," writes Dr Dominique Deplanque, of the Department of Pharmacology at the University of Lille.

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